This invention is related to the control of space heating system with the forced circulation of hot water from the central heating source to a space heating units. An object of invention is to solve the problem of discrepancy between building space heating losses and heat supply and to improve building comfort while reducing fuel consumption and saving energy.
The main purpose of space heating system is to provide the desired inside room air temperature at different outside conditions. In general, the building room heat losses change proportionally to the difference between the room and outside air temperatures. This is true when the consideration is taken for a building steady state heat mode, for example, for a daily average outside air temperature. For current outside temperature conditions it is not necessarily so because the outside air temperature changes during a day making an oscillation around the daily averaged air temperature. Some of the components of a building heat losses do not immediately follow these momentary air temperature changes, among them are heat losses through the outside inertial exposures such as walls, floor, roof. Meanwhile, heat losses by a non inertial exposures such as windows, doors and by infiltration and ventilation - exactly follow the change of momentary outside air temperature. The total building heat losses, due to the impact of unsteady state heat mode, for the most of the time, do not follow the momentary outside air temperature changes, however, these factors generally are not considered. In practice, because of the thermal inertia of building's exposures and heating systems the heat supply provided from the heating system differs from the heat loss of the room, causing the deviation of room air temperature from its design conditions. The closer the amount of heat supply is to the amount of heat losses in the room, the less this deviation will be and, as a result, there will be more comfortable room conditions and there will be less fuel spent, when the other conditions are assumed as equal. The sample of illustration of influence of building thermal inertia on the room air temperature oscillation is shown in the FIGS. 1a, 1b and 1c. The data shown in these figures is related to the typical classroom in a school building which has a medium inertial construction. The infiltration rate for the room is 0.27 air change per hour (ACH). In FIG. 1a the daily changes of outside air temperature are shown. The design value of oscillation amplitude of outside air temperature is assumed as 11.degree. F. It is not uncommon to find much greater value of design outside air temperature oscillation amplitude in a real conditions. It may become as much as two-three times higher than the value taken in this example. Also, in this figure the oscillation of room space heating losses and room space heating supply (following the momentary outside air temperature changes) are shown. It is seen that heat supply and heat losses do not concur with each other. This is because the room heat losses do not follow the momentary changes of outside air temperature due to the room thermal response. Although the room heat losses have an insignificant time lag, compare to the heat supply, their oscillation amplitude is less than the amplitude of heat supply in 1.6 times (FIG. 1b). The discrepancy between these two is shown by the dashed line which represents subtraction of heat losses from the heat supply. This resulted in a room air temperature amplitude (FIG. 1c) which is close to 0.5.degree. F. (room air temperature departure from its design value). In FIGS. 2a and 2b the results of calculation of classroom temperature oscillation amplitude for the different control strategies and for the different values of ACH are given. The control of heat supply is done following to a momentary outside air temperature changes (N.sub.M.O. =1) or to a temperature of the suggested device--outside air temperature converter (load anticipator), which is characterized by a change of N.sub.S.D. value from 1.2 to N.sub.S.D. =2 (that is equivalent to the artificial decreasing of outside air temperature oscillation amplitude, respectively in 1.2 and 2 times). For the convenience of analysis the changes of room temperature are given as a relative values (the ratio of considered value to the value, which is conditionally assumed as 1). It can be seen from the FIG. 2a than control of heat supply at 0.27 ACH by the temperature of the outside air temperature converter is more efficient than following a momentary outside air temperature. Optimal value N.sub.S.D. =2.0 reduces the room air temperature oscillation in 1.7 times and leads to a better room comfort conditions. It can be proved, that the reduction of room air temperature fluctuation is directly translated to energy savings. This is so due to the elimination of undesirable room air temperature fluctuation below the comfort level. Otherwise, the temperature level in the room should be increased to satisfy a given comfort requirements. The calculations conducted for the same room (FIG. 2b) have shown that increasing the value of ACH to 2.5 (because of intensive operation of mechanical ventilation system) will switch the better control strategy from following the outside air temperature converter to a momentary outside air temperature N.sub.M.O =1. In this particular case control by a momentary outside air temperature leads to a reduction of room temperature amplitude in comparison with suggested device. It can be shown, that when in the considered building mechanical ventilation is not used intensively (approximately 1.5 ACH), a space heating control following either momentary outside air temperature change or temperature of outside air temperature converter virtually gives the same level of comfort. For both control strategies a value of oscillation of room air temperature is quite similar.
From a given above analysis it is obvious, that combined boiler water temperature control with consideration of both steady state and unsteady state building heat modes provides the best results for a buildings with different levels of people occupancy during a day. In that type of buildings (schools and institutional buildings) people attendance changes from minimum (night time and weekends) to a maximum occupancy schedule (during weekdays). In periods with high ventilation load (maximum number of people attendance) the space heating control should be following the momentary outside air temperature measured by the exposed to ambient thermometer. At the same time, during the periods with lower level of people occupancy or when the buildings are closed it is beneficial to consider the building unsteady state heat mode and to use the outside air temperature converter for space heating control. During this particular time the boiler water temperature oscillation can be significantly reduced, in comparison with control following momentary outside air temperature, with a simultaneous fuel savings. For other buildings, such as apartment complexes, residential houses, commercial offices and etc., without mechanical ventilation the space heating control always should be implemented by following the values measured by an outside air temperature converter (load anticipator). As the calculation has shown, to match the unsteady state heat mode of majority of the buildings this load anticipator should be able to artificially reduce outside air temperature oscillation amplitude in 1.5-3 times. Also, the use of outside air temperature converter reduces the boiler overcontrol and eliminates otherwise frequent boiler cycling (from on to off) as the result of providing closer match of heat supply to the actual building heat losses. This will lead to energy savings due to the reduction of boilers' stand by losses. To total all that have been said above, the present invention will contribute: to a better building comfort conditions, to reduction of fuel consumption on space heating, to providing for a space heating system optimal operation, as well as for its dependability and durability.